Along with the widespread use of a digital camera, e.g. a camera-equipped cell phone and the like, the market for solid-state imaging apparatuses has been remarkably developed. In this flow of development, needs have changed to the development of a highly sensitive and a high pixel solid-state imaging apparatus. In recent years, following the development of a thin digital still camera and a thin cell phone, there is an increasing need for thinning the camera portion. In other words, a lens used for the camera portion has a short focal length, which means that light enters a solid-state imaging apparatus with a wide angle (a wide angle measured from a vertical axis of an incidence plane of the solid-state imaging apparatus).
At present, in a charged-coupled device (CCD) and a metal oxide semiconductor (MOS) imaging sensor that are commonly used as solid-state imaging apparatuses, semiconductor integrated circuits having plural light-receiving portions are arranged in a two-dimensional array, in which an optical signal from an object is converted into an electric signal.
The sensitivity of the solid-state imaging apparatus is defined based on the amount of output current of a light-receiving element to the amount of incident light. Therefore, leading the incident light reliably into the light-receiving element is an important factor for the improvement of sensitivity.
FIG. 4 is a diagram showing an example of a conventional fundamental structure of a general pixel. As shown in FIG. 4, light 59 (light indicated by dashed lines) which enters vertically into a microlens 61 is dispersed into colors through one of red (R), green (G), and blue (B) color filters 2, and then converted into an electric signal by a light-receiving unit 6. Since relatively high light-condensing efficiency can be obtained, this microlens 61 is used in almost all solid-state imaging apparatuses.
An example of a structure in which a lens of each pixel is asymmetrically arranged in the solid-state imaging apparatus using the microlenses has been suggested (e.g. refer to Japanese Laid-Open Patent Application No. 2001-196568 (JP'568). JP'568 discloses an embodiment in which oblique incident light can be introduced to a sensing unit.
Furthermore, various technologies are disclosed as a solid-state imaging apparatus using Fresnel lenses (e.g. refer to Japanese Laid-Open Patent Application No. 2000-39503 (JP'503) and Japanese Laid-Open Patent Application No. 5-251673 (JP'673).
In the technology disclosed in JP'503, a lens is made up of multiple layers which have different refractive indexes and are shaped into concentric circles, and the center part has the highest refractive index as the refractive index decreases towards the peripheral part of the concentric circle structure. Furthermore, in the technology disclosed in the JP'673, a thickness distribution type lens and a distributed refractive index type lens which has a consecutive refractive index distribution through doping are used.    Patent Reference 1: Japanese Laid-Open Patent Application No. 2001-196568    Patent Reference 2: Japanese Laid-Open Patent Application No. 2000-39503    Patent Reference 3: Japanese Laid-Open Patent Application No. 5-251673
To develop a solid-state imaging apparatus corresponding to a wide angle incident, it is necessary to lead the incident light incoming with a particular angle reliably to a light-receiving element.
However, in the microlens, the light-condensing efficiency decreases as the incident angle increases. In other words, as shown in FIG. 4, while the light 59 incoming vertically into the microlens 61 can be condensed very efficiently, the light-condensing efficiency for oblique incident light 60 incoming diagonally (light indicated by solid lines) into the lens decreases. This is because the oblique incident light 60 is blocked by Al wirings 3 in a pixel so that it cannot reach up to the light-receiving element 6.
As previously described, the solid-state imaging apparatus is made up of multiple pixels that are arranged in a two dimensional array. Therefore, in the case of incident light with a spread angle, the angle of incidence differs between the central pixels and the peripheral pixels (see FIG. 1). As a result, the light-condensing efficiency of the peripheral pixels decreases more than that of the central pixels.
FIG. 2 is a diagram showing an example of a conventional structure of a pixel positioned in the periphery. The incident angle of the incident light is large at pixels in the periphery. Therefore, the improvement of the light-condensing efficiency is sought by displacing (shrinking) electric wiring portions toward an inward direction of the center of the solid-state imaging apparatus.
FIG. 3 is a diagram showing a dependency on incident angles of the light-condensing efficiency in the conventional solid-state imaging apparatus using microlens. As shown in FIG. 3, it can be seen that the light with an incident angle up to 20° can be condensed highly efficiently. However, the light-condensing efficiency rapidly decreases as the incident angle becomes higher than 20°. As a result, currently, the amount of light condensed in the peripheral pixels is about 40 percent of that in the central pixels, and the sensitivity of entire pixels is limited by the sensitivity of the peripheral pixels. This value further decreases along with the decrease in the pixel size so that its application to an optical system with a short focal length such as a small camera becomes very difficult. Furthermore, in a manufacturing method thereof, there is a problem that further circuit shrinking cannot be realized.
In addition, in the case where finely shaped steps such as Fresnel lens shapes are found on the surface of the solid-state imaging apparatus, there is a problem that, especially, dusts from dicing processing are deposited in a shape of finely shaped steps when the solid-state imaging apparatus is manufactured.
Furthermore, in the case where finely shaped steps such as Fresnel lens shapes are found on the surface of the solid-state imaging apparatus, a color filter cannot be placed on top of the light-collecting device.
Accordingly, considering the aforementioned problems, it is an object of the present invention to provide an optical device structure which can condense light incoming with a higher angle than the existing microlens, and to provide a structure which does not cause a problem of dust deposition, in order to realize a solid-state imaging apparatus applicable to an optical system (an optical system with a high incident angle θ) with a short focal length for a thin camera.
In order to solve the aforementioned problem, a light-collecting device according to the present invention is a light-collecting device including an aggregate of light-transmitting films having different refractive indexes, wherein one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned.
Accordingly, a distributed refractive index light-collecting device, which can change effective refractive indexes, can be realized by changing the line width and arrangement density of the one light-transmitting film. Furthermore, following the conventional semiconductor process, a fine distributed refractive index lens can be manufactured.
Furthermore, the one light-transmitting film is buried in the other light-transmitting film. Accordingly, it can be prevented that dusts are deposited on the top surface of the light-collecting device.
Also, an optical center of the aggregate is located at a position displaced from a center of said light-collecting device. Furthermore, in the case where Φ(x) is a phase modulation depending on a distance x in an in-plane direction in the aggregate, the following equation,Φ(x)=Ax2+Bx sin θ+2 mπ
is approximately satisfied, where θ is an incident angle of the incident light, A and B are predetermined constants, and m is a natural number.
Accordingly, the propagation direction of light incident at a specific angle can be easily controlled so that the incident light can be condensed at an arbitral position.
Furthermore, in the light-collecting device, a difference between a refractive index of the one light-transmitting film and a refractive index of the other light-transmitting film may be 0.1 or greater. Accordingly, a distributed refractive index type light-collecting device, which can change effective refractive indexes, can be realized.
Furthermore, the refractive index of the one light-transmitting film is a value in a range from 1.45 to 3.4. Thus, using the high refractive index material, the film thickness of the light-transmitting film can be thinned so that the manufacturing process can be facilitated.
Furthermore, the refractive index of the one light-transmitting film may be greater than the refractive index of said other light-transmitting film, or the refractive index of the one light-transmitting film may be smaller than the refractive index of the other light-transmitting film.
Furthermore, a light-transmitting material for the one light-transmitting film or the other light-transmitting films is air. Consequently, the dynamic range of the refractive index distribution is increased and the light-condensing efficiency of the lens can be improved.
Furthermore, the one light-transmitting film or the other light-transmitting film further has, in a vertical direction, a multi-layered structure made of light-transmitting materials having different refractive indexes. Accordingly, gradation of the refractive indexes is increased and the high-efficient distributed refractive index lens can be manufactured.
Furthermore, a light-transmitting material for the one light-transmitting film or the other light-transmitting film varies in type or arrangement depending on a wavelength of the incident light or a wavelength of a representative light of the incident light. Consequently, a structure of a lens of each pixel can be optimized in accordance with a wavelength of the incident light so that a difference of light-condensing efficiency depending on a color can be avoided.
Furthermore, in the light-collecting device, a light-transmitting material for the one light-transmitting film or the other light-transmitting film varies in type or arrangement depending on a focal length set for the incident light. Consequently, the focal length of the incident light can be changed so that a lens which is appropriate to each pixel structure can be designed.
In the case where Δn(x) is a difference between a refractive index of the aggregate and a refractive index of a light-incoming side medium, which depends on a distance x in an in-plane direction in the aggregate, the aggregate approximately satisfies the following equation,Δn(x)=Δnmax[(Ax2+Bx sin θ)/2π+C]
where θ is an incident angle of the incident light, Δnmax is a maximum value of the difference between the refractive index of said aggregate and the refractive index of the light-incoming side medium, and A, B and C are predetermined constants. Accordingly, a distributed refractive index lens with high light-condensing efficiency which can condense light incident at a specific angel at an arbitral position can be manufactured.
Furthermore, in the light-collecting device, in the case where a thickness of the aggregate is L, and a wavelength of the incident light is λ, the following equationΔnmaxL=λ
may be approximately satisfied. Accordingly, the maximum phase modulation by the distributed index lens corresponds to one phase of the incident light and the light-collecting loss becomes the minimum. Therefore, high efficient light collecting can be achieved.
Furthermore, in the light-collecting device, a shape of a cross section of the one light-transmitting film or the other light-transmitting film in a normal direction is rectangular. Consequently, a high precision refractive index change in compliance with a design can be realized and a high sensitive solid-state imaging apparatus can be structured.
Furthermore, in the light-collecting device, the one light-transmitting film or the other light-transmitting film is made of a light-transmitting material with a diameter which is equal to or smaller than the wavelength of the incident light. Using this method, a distributed refractive index element can be easily manufactured by changing effective refractive indexes by changing particle size of adjacent light-transmitting materials.
Furthermore, in the light-collecting device, the one light-transmitting film includes one of TiO2, ZrO2, Nb2O5, Ta2O5, Si3N4 and Si2N3. Since they are high refractive index materials, a thickness of the light-transmitting film can be thinned, and a manufacturing process can be facilitated.
Furthermore, in the light-collecting device, the one light-transmitting film includes one of SiO2 doped with B or P, that is Boro-Phospho Silicated Glass, and Teraethoxy Silane. They are materials generally used in a conventional semiconductor process. Therefore, a light-collecting device can be easily manufactured, and manufacturing costs can be reduced.
Furthermore, in the light-collecting device, the one light-transmitting film includes one of benzocyclobutene, polymethymethacrylate, polyamide and polyimide. Since such resins allow direct processing, a light-collecting device can be manufactured by nanoimprinting and mass production can be encouraged.
Furthermore, a solid-state imaging apparatus according to the present invention is a solid-state imaging apparatus which includes unit pixels arranged in a two-dimensional array, in which each unit pixel has a light-collecting device which has an aggregate of light-transmitting films having different refractive indexes. Here, one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned.
Accordingly, a solid-state imaging apparatus which includes a distributed refractive index type light-collecting device, which can change the effective refractive indexes, can be realized by changing a line width and arrangement density of the one light-transmitting film. Furthermore, following the conventional semiconductor process, a fine distributed refractive index lens can be manufactured.
While in the solid-state imaging apparatus, a color filter is positioned above the aggregate, a color filter may also be positioned below the aggregate.
Furthermore, a type or an arrangement of a light-transmitting material of the light-transmitting film differs between (a) the one light-transmitting film or the other light-transmitting film of a unit pixel located in a center of the solid-state imaging apparatus and (b) the one light-transmitting film or the other light-transmitting film of a unit pixel located in a periphery of the solid-state imaging apparatus. Consequently, a structure of a lens can be optimized depending on positions of pixels on the solid-state imaging apparatus, so that sensitivity of entire element is increased. Furthermore, since the shrinking structure of the solid-state imaging apparatus can be eased, the method of manufacturing the solid-state imaging apparatus is facilitated.
Furthermore, the aggregate of the solid-state imaging apparatus is formed so as to cover an entirety of a corresponding unit pixel. Consequently, the light-condensing loss between pixels is reduced and the sensitivity of the solid-state imaging apparatus can be improved.
Furthermore, a method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes a process of forming the aggregate by nanoimprinting using a mold for a minimum processing dimension of 1 nm or less. Consequently, a large amount of fine concentric structure can be manufactured easily. Furthermore, displacements of the relative positions between pixels are prevented and the steps for the adjustment operation are reduced. Therefore, a low-priced optical device can be realized.
Furthermore, a method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes a process of forming the aggregate by one of electron beam rendering and light beam rendering. Consequently, a conventional semiconductor process can be used and an ultra-fine structure can be manufactured. Therefore, an optical element with high light-condensing efficiency can be obtained.
Furthermore, a method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes a process of forming the aggregate by autoagglutination of particles, each of the particles having particle size which is equal to or smaller than a wavelength of the incident light. Consequently, the number of processing steps can be reduced, and the manufacturing costs can be reduced.
Furthermore, a method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes: a process of forming, on an Si substrate, a semiconductor integrated circuit which includes a light-receiving element, wiring, a light-blocking layer and a signal transmitting unit; a process of stacking a first light-transmitting film on the semiconductor integrated circuit; a process of stacking a second light-transmitting film on the first light-transmitting film; a process of processing the second light-transmitting film so as to have a concentric circle structure; a process of forming a resist on the second light-transmitting film; and a process of etching the first light-transmitting film using the second light-transmitting film as a mask. Accordingly, a lens structure in compliance with a design can be easily manufactured by setting the positional precisions of the first layer and the second layer at closer to 0. Therefore, a device with high light-condensing efficiency can be realized.
A method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes: a process of forming, on an Si substrate, a semiconductor integrated circuit which includes a light-receiving element, wiring, a light-blocking layer and a signal transmitting unit; a process of forming a first light-transmitting film on the semiconductor integrated circuit, the first light-transmitting film including a first light-transmitting material and a second light-transmitting material; a process of stacking a second light-transmitting film on the first light-transmitting film; a process of processing the second light-transmitting film so as to have a concentric circle structure; a process of forming resist on the second light-transmitting film; a process of etching an interface between the first light-transmitting material and the second light-transmitting material that are included in the first light-transmitting film, using the second light-transmitting film as a mask; a process of embedding the first light-transmitting material into an air hole of the first light-transmitting film; and a process of planarizing the second light-transmitting film. Accordingly, since the material interface of the first layer is approximately matches the material interface of the second layer. Therefore, a high precision refractive index distribution can be manufactured and an element with a high light-condensing efficiency can be realized.
A method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes: a process of forming, on an Si substrate, a semiconductor integrated circuit which includes a light-receiving element, wiring, a light-blocking layer and a signal transmitting unit; a process of stacking a first light-transmitting film on the semiconductor integrated circuit; a process of stacking a second light-transmitting film on the first light-transmitting film; a process of processing the second light-transmitting film so as to have a concentric circle structure; a process of forming resist on the second light-transmitting film; and a process of performing isotropic etching on the first light-transmitting film using the second light-transmitting film as a mask. Consequently, gradation of the refractive index distribution can be increased and the light-condensing efficiency can be also increased.
Furthermore, a method of manufacturing a solid-state imaging apparatus according to the present invention is a method of manufacturing a solid-state imaging apparatus including an aggregate of light-transmitting films having different refractive indexes, in which one light-transmitting film in the aggregate has a concentric circle shape with a predetermined thickness and a width which is equal to or smaller than a wavelength of incident light, and an other light-transmitting film in the aggregate concentrically fills all or a part of a space of the aggregate in which the one light-transmitting film is not positioned. Here, the method includes: a process of forming, on an Si substrate, a semiconductor integrated circuit which includes a light-receiving element, wiring, a light-blocking layer and a signal transmitting unit; a process of forming a first light-transmitting film on the semiconductor integrated circuit, the first light-transmitting film including a first light-transmitting material and a second light-transmitting material; a process of stacking a second light-transmitting film on the first light-transmitting film; a process of processing the second light-transmitting film so as to have a concentric circle structure; a process of forming resist on the second light-transmitting film; a process of performing isotropic etching an interface between the first light-transmitting material and the second light-transmitting material that are included in the first light-transmitting film, using the second light-transmitting film as a mask; a process of embedding the first light-transmitting material into an air hole of the first light-transmitting film; and a process of planarizing the second light-transmitting film.
Furthermore, a method of manufacturing a solid-state imaging apparatus includes a step of etching a material interface of the light-transmitting film made of the first and second materials, using etchant, to respective first and second materials, having different etching rates. Consequently, the volume ratio can be controlled uniquely to a material and gradation of the distribution can be further increased. Therefore, light-condensing efficiency can be improved.
A solid-state imaging apparatus of the present invention has the lens structure described in the above so that improvements of its degree of resolution and sensitivity and an easier manufacturing method can be realized. Furthermore, the deposition of dusts into fine shape can be prevented.